One method to operate an internal combustion engine having a turbocharger is presented in U.S. Pat. No. 6,202,414. This method presents a way to balance the output of two turbochargers that are in communication with different cylinder banks of a “V” engine. Balancing the output of two turbochargers can improve turbocharger efficiency and mitigate the possibility of compressor surge. This method uses state parameters that are in the vicinity of the turbocharger compressors to adjust the effective turbine cross section, thereby regulating compressor flow. The method attempts to reduce any difference in state parameters between two cylinder groups to zero. That is, the method attempts to equalize the state parameters of the two cylinder groups that are in communication with the two turbochargers.
The above-mentioned method can also have a disadvantage. Namely, the method only has a capacity to regulate compressor flow by adjusting the position of a waste gate. However, waste gates typically require a minimum level of compressor flow to overcome the spring force that normally holds a waste gate in a closed position. Therefore, it is not possible to regulate compressor flow when the pressure to overcome the spring force is not being developed at the compressor outlet. Consequently, it remains possible to encounter compressor surge conditions even when the method is used as described.
The inventors herein have recognized the above-mentioned disadvantage and have developed a method to control a turbocharged engine having variable valve operation.